Editing Homothallism

'''Homothallic''' refers to the possession, within a single organism, of the resources to reproduce sexually;<ref name="urlOn-Line Glossary: H">{{cite web|url=http://www.plantpath.cornell.edu/glossary/Defs_H.htm |archive-url=https://web.archive.org/web/20060908130055/http://www.plantpath.cornell.edu/glossary/Defs_H.htm |url-status=dead |archive-date=2006-09-08 |title=On-Line Glossary: H |access-date=2008-10-24 }}</ref> i.e., having male and female reproductive structures on the same [[thallus]]. The opposite sexual functions are performed by different cells of a single mycelium.<ref>{{cite web|url=https://www.thefreedictionary.com/Homothallic|title=Homothallic|access-date=16 January 2018|via=The Free Dictionary}}</ref>

Sexual reproduction commonly occurs in two fundamentally different ways in fungi. These are outcrossing (in heterothallic fungi) in which two different individuals contribute nuclei to form a zygote, and self-fertilization or selfing (in homothallic fungi) in which both nuclei are derived from the same individual. Homothallism in [[fungus|fungi]] can be defined as the capability of an individual spore to produce a [[sexual reproduction|sexually reproducing]] colony when propagated in isolation.<ref name = Wilson2015>{{cite journal | vauthors = Wilson AM, Wilken PM, van der Nest MA, Steenkamp ET, Wingfield MJ, Wingfield BD | title = Homothallism: an umbrella term for describing diverse sexual behaviours | journal = IMA Fungus | volume = 6 | issue = 1 | pages = 207–14 | date = June 2015 | pmid = 26203424 | pmc = 4500084 | doi = 10.5598/imafungus.2015.06.01.13 }}</ref> Homothallism occurs in fungi by a wide variety of genetically distinct mechanisms that all result in sexually reproducing cultures from a single cell.<ref name = Wilson2015/>

Among the 250 known species of aspergilli, about 36% have an identified sexual state.<ref name=Dyer>{{cite journal | vauthors = Dyer PS, O'Gorman CM | title = Sexual development and cryptic sexuality in fungi: insights from Aspergillus species | journal = FEMS Microbiology Reviews | volume = 36 | issue = 1 | pages = 165–92 | date = January 2012 | pmid = 22091779 | doi = 10.1111/j.1574-6976.2011.00308.x | doi-access = free }}</ref> Among those ''[[Aspergillus]]'' species for which a sexual cycle has been observed, the majority in nature are homothallic (self-fertilizing).<ref name=Dyer /> Selfing in the homothallic fungus ''[[Aspergillus nidulans]]'' involves activation of the same mating pathways characteristic of sex in outcrossing species, i.e. self-fertilization does not bypass required pathways for outcrossing sex but instead requires activation of these pathways within a single individual.<ref name="pmid17669651">{{cite journal | vauthors = Paoletti M, Seymour FA, Alcocer MJ, Kaur N, Calvo AM, Archer DB, Dyer PS | title = Mating type and the genetic basis of self-fertility in the model fungus Aspergillus nidulans | journal = Current Biology | volume = 17 | issue = 16 | pages = 1384–9 | date = August 2007 | pmid = 17669651 | doi = 10.1016/j.cub.2007.07.012 | doi-access = free | bibcode = 2007CBio...17.1384P }}</ref> Fusion of haploid nuclei occurs within reproductive structures termed [[Ascocarp|cleistothecia]], in which the [[Ploidy#Diploid|diploid]] [[zygote]] undergoes [[Meiosis|meiotic]] divisions to yield [[Ploidy#Haploid and monoploid|haploid]] [[ascospores]].

Several [[ascomycota|ascomycete]] fungal species of the genus ''[[Cochliobolus]]'' (''[[Cochliobolus luttrellii|C. luttrellii]]'', ''[[Cochliobolus cymbopogonis|C. cymbopogonis]]'', ''[[Cochliobolus kusanoi|C. kusanoi]]'' and ''[[Cochliobolus homomorphus|C. homomorphus]]'') are homothallic.<ref name="pmid10318929">{{cite journal | vauthors = Yun SH, Berbee ML, Yoder OC, Turgeon BG | title = Evolution of the fungal self-fertile reproductive life style from self-sterile ancestors | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 96 | issue = 10 | pages = 5592–7 | date = May 1999 | pmid = 10318929 | pmc = 21905 | doi = 10.1073/pnas.96.10.5592 | bibcode = 1999PNAS...96.5592Y | doi-access = free }}</ref> The ascomycete fungus ''[[Pneumocystis jirovecii]]'' is considered to be primarily homothallic.<ref name="pmid29463658">{{cite journal | vauthors = Richard S, Almeida JM, Cissé OH, Luraschi A, Nielsen O, Pagni M, Hauser PM | title = Pneumocystis MAT Genes Suggest Obligate Sexuality through Primary Homothallism within Host Lungs | journal = mBio | volume = 9 | issue = 1 | date = February 2018 | pmid = 29463658 | pmc = 5821091 | doi = 10.1128/mBio.02201-17 }}</ref> The ascomycete fungus ''Neosartorya fischeri'' is also homothallic.<ref name="pmid17384199">{{cite journal | vauthors = Rydholm C, Dyer PS, Lutzoni F | title = DNA sequence characterization and molecular evolution of MAT1 and MAT2 mating-type loci of the self-compatible ascomycete mold Neosartorya fischeri | journal = Eukaryotic Cell | volume = 6 | issue = 5 | pages = 868–74 | date = May 2007 | pmid = 17384199 | pmc = 1899244 | doi = 10.1128/EC.00319-06 }}</ref> ''Cryptococcus depauperatus'', a homothallic [[basidiomycota|basidiomycete]] fungus, grows as long, branching filaments (hyphae).<ref name = Passer2022>{{cite journal |vauthors=Passer AR, Clancey SA, Shea T, David-Palma M, Averette AF, Boekhout T, Porcel BM, Nowrousian M, Cuomo CA, Sun S, Heitman J, Coelho MA |title=Obligate sexual reproduction of a homothallic fungus closely related to the Cryptococcus pathogenic species complex |journal=eLife |volume=11 |issue= |pages= |date=June 2022 |pmid=35713948 |pmc=9296135 |doi=10.7554/eLife.79114 |doi-access=free }}</ref> ''C. depauperatus'' can undergo [[meiosis]] and [[sexual reproduction|reproduce sexually]] with itself throughout its life cycle.<ref name = Passer2022/>

A [[lichen]] is a composite organism consisting of a [[fungus]] and a [[Photosynthesis|photosynthetic]] partner that are growing together in a [[Symbiosis|symbiotic]] relationship. The photosynthetic partner is usually either a [[Green algae|green alga]] or a [[Cyanobacteria|cyanobacterium]]. Lichens occur in some of the most extreme environments on Earth—[[Tundra#Arctic|arctic tundra]], hot [[desert]]s, rocky coasts, and toxic [[Slag|slag heaps]]. Most lichenized fungi produce abundant sexual structures and in many species sexual spores appear to be the only means of dispersal (Murtagh et al., 2000). The lichens ''Graphis scripta'' and ''Ochrolechia parella'' do not produce symbiotic vegetative propagules. Rather the lichen-forming fungi of these species reproduce sexually by self-fertilization (i.e. they are homothallic), and it was proposed that this breeding system allows successful reproduction in harsh environments (Murtagh et al., 2000).<ref name="pmid10766229">{{cite journal | vauthors = Murtagh GJ, Dyer PS, Crittenden PD | title = Sex and the single lichen | journal = Nature | volume = 404 | issue = 6778 | pages = 564 | date = April 2000 | pmid = 10766229 | doi = 10.1038/35007142 | s2cid = 4425228 }}</ref>

Homothallism appears to be common in natural populations of fungi. Although self-fertilization employs meiosis, it produces minimal genetic variability. Homothallism is thus a form of sex that is unlikely to be adaptively maintained by a benefit related to producing variability. However, homothallic meiosis may be maintained in fungi as an adaptation for surviving stressful conditions; a proposed [[Meiosis|benefit of]] [[Meiosis#Theory that DNA repair is the adaptive advantage of meiosis|meiosis]] is the promoted [[Homologous recombination|homologous meiotic recombinational]] repair of DNA damages that are ordinarily caused by a stressful environment.<ref name="pmid3324702">{{cite book | vauthors = Bernstein H, Hopf FA, Michod RE | title = Molecular GeneticsofDevelopment | chapter = The molecular basis of the evolution of sex | series = Advances in Genetics | volume = 24 | pages = 323–70 | date = 1987 | pmid = 3324702 | doi = 10.1016/s0065-2660(08)60012-7 | isbn = 9780120176243 }}</ref>

== Evolution ==

{{Main|Evolution of sexual reproduction}}

{{Expand section|date=August 2021}}

Homothallism evolved repeatedly from [[heterothallic|heterothallism]].<ref>{{Cite book|last1=Beukeboom|first1=Leo W.|url=https://books.google.com/books?id=7yrnAwAAQBAJ&q=mating+types+evolved|title=The Evolution of Sex Determination|last2=Perrin|first2=Nicolas|date=2014|publisher=Oxford University Press|isbn=978-0-19-965714-8|pages=50|language=en}}</ref>

* [[Hermaphroditism]]

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[[Category:Mycology]]